1. Field of the Invention
This invention relates to improved rubber products with better abrasion resistance. More particularly, this invention concerns the use of nitrile rubbers, in particularly, carboxylated nitrile rubbers with proper additives to make long life rubber products, e.g., rice hulling rolls.
2. Brief Description of the Prior Art
It is known in the art that current hulling rolls are made of styrene-butadiene rubber (SBR) with proper additives. Typically SBR needs sulfur, accelerators, antioxidants, antiozonants, activators, fillers, and softeners or extenders. The ingredients are mixed in internal mixers or on mills, and calendered, molded and cured in conventional equipment. Mixing procedures vary with the compounds. In general, the rubber, zinc oxides, antioxidant, and stearic acid are mixed; then the filler is added in portions with the softeners or oil. For rice hulling rolls, in order to maintain the quality of the rice, Hi-Sil is usually used as the filler instead of carbon black. It is general practice to dump and cool the batch. The second phase includes mixing in all the other ingredients, with the accelerator and sulfur being added last. Mixing is continued until the sulfur is well dispersed. The hulling rolls are usually produced from stock. First the core must be carefully applied to the core and rolled down by machine or by hand. Special care must be taken to prevent the incorporation of air into the roll either between the plies or as blisters in the calendered stock. The roll is built to sufficient size to allow it to be ground to a smooth surface at the desired diameter. The built roll is then wrapped tightly with nylon tape for vulcanization in an open steam. The vulcanized roll, after cooled, is machined to the proper size. The SBR rubber roll made as described above is currently used in all the rice mills. It is obvious that the rice hulling depends on abrasion to strip the rice shell. Further, in the hulling process, heat is generated. It is well known that the SBR roll does not have good heat resistance. When the shelling temperature is increased, the roll life will be decreased.